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United States Patent |
5,318,933
|
Sundell
,   et al.
|
June 7, 1994
|
Carbon-containing carbon bonded refractories with improved physical
properties
Abstract
Carbon-containing carbon bonded refractory mixes and products made
therefrom in which the refractory is a magnesite or high alumina aggregate
and containing a silica-free elemental boron containing B-Mg-O alloy
powder containing at least 95% B-Mg-O. and shapes made therefrom. The
invention also involves the method of increasing the lining life of a
metallurgical vessel utilizing unburned brick made from the above-noted
mixes.
Inventors:
|
Sundell; David R. (Pittsburgh, PA);
Whittemore; Dwight S. (Bethel Park, PA)
|
Assignee:
|
Indresco Inc. (Dallas, TX)
|
Appl. No.:
|
036151 |
Filed:
|
March 24, 1993 |
Current U.S. Class: |
501/100; 501/101; 501/109 |
Intern'l Class: |
C04B 035/52 |
Field of Search: |
501/100,101,109
|
References Cited
U.S. Patent Documents
4306030 | Dec., 1981 | Watanabe et al.
| |
4471059 | Sep., 1984 | Yoshino et al.
| |
4540675 | Sep., 1985 | Morris et al.
| |
4605635 | Aug., 1986 | Zenbutsu et al.
| |
4912068 | Mar., 1990 | Michael et al.
| |
4957887 | Sep., 1990 | Michael et al.
| |
Foreign Patent Documents |
60-108362 | Jun., 1985 | JP.
| |
127124 | May., 1989 | JP.
| |
Primary Examiner: Group; Karl
Attorney, Agent or Firm: Sigalos; John L.
Claims
What is claimed is:
1. A carbon-containing refractory mix comprising at least about 70 wt. % of
a magnesite or high alumina aggregate, a carbon containing material, a
silica-free elemental boron containing B-Mg-O alloy powder in an amount up
to about 10 wt. %, and for each 100 wt. % thereof, from about 1 to 6 wt. %
of a carbonaceous bonding agent, said magnesite containing at least about
95% MgO, said alumina aggregate containing at least about 47.5% alumina,
said carbon containing material containing at least about 90% carbon, said
alloy containing at least 95% B+Mg+O.
2. The mix of claim 1 wherein said mix contains about 70 to 97 wt. % of
magnesite containing at least 95 wt. % magnesia and is either deadburned,
fused or a combination thereof, said carbon containing material is flake
graphite in an amount of about 3 to 30 wt. %, and said alloy powder is
present in an amount of 0.05 to 10 wt. %.
3. The mix of claim 2 wherein said flake graphite is replaced by carbon
black or calcined coke in amounts up to 100% of the total flake graphite
content.
4. The mix of claim 3 wherein said boron alloy contains at least 95 wt. %
boron, magnesium, and oxygen in the form of amorphous or crystalline boron
and magnesium borate, the boron content of the alloy being in range of
about 5 to 75 wt. %, and the particle size of the alloy powder is -200
mesh.
5. The mix of claim 4 also containing aluminum, silicon, magnesium, boron
carbide, boron nitride, silicon carbide, silicon nitride, or combinations
thereof in an amount up to 10 wt. %.
6. The mix of claim 5 wherein said carbonaceous binder is a novolak resin,
a resole resin, tar, pitch, or mixtures thereof.
7. An unburned magnesite-carbon refractory shape consisting essentially of
the mix of claim 1 formed into a shape and baked.
8. The refractory shape of claim 7 wherein said mix contains about 70 to 97
wt. % of a magnesite containing at least 95 wt. % magnesia and is either
deadburned, fused or a combination thereof, said carbon containing
material is graphite in an amount of about 3 to 30 wt. %, and said alloy
powder is present in an amount of 0.05 to 10 wt. %.
9. The refractory shape of claim 8 wherein said flake graphite is replaced
by carbon black or calcined coke in amounts up to 100% of the total flake
graphite content.
10. The refractory shape of claim 9 wherein said boron alloy contains at
least 95 wt. % boron, magnesium, and oxygen in the form of amorphous or
crystalline boron and magnesium borate, the boron content of the alloy
being in range of about 5 to 75 wt. %, and the particle size of the alloy
powder is -200 mesh.
11. The refractory shape of claim 10 wherein said mix also contains
aluminum, silicon, magnesium, boron carbide, boron nitride, silicon
carbide, or silicon nitride, or combinations thereof in an amount up to 10
wt. %.
12. The refractory shape of claim 11 wherein said carbonaceous binder is a
novolak resin, a resole resin, tar, pitch, or mixtures thereof.
13. An unburned refractory brick consisting essentially of the mix of claim
1 formed in the shape of a brick and baked.
14. The brick of claim 13 wherein said mix contains about 70 to 97 wt. % of
a magnesite containing at least 95 wt. % magnesia and is either
deadburned, fused or a combination thereof, said carbon containing
material is flake graphite in an amount of about 3 to 30 wt. %, and said
alloy powder is present in an amount of 0.05 to 10 wt. %.
15. The brick of claim 14 wherein said flake graphite is replaced by carbon
black or calcined coke in amounts up to 100% of the total flake graphite
content.
16. The brick of claim 15 wherein said boron alloy contains at least 95 wt.
% boron, magnesium, and oxygen in the form of amorphous or crystalline
boron and magnesium, borate, the boron content of the alloy being in range
of about 5 to 75 wt. %, and the particle size of the alloy powder is -65
mesh.
17. The brick of claim 16 wherein said mix also contains aluminum, silicon,
magnesium, boron carbide, boron nitride, silicon carbide, or silicon
nitride, or combinations thereof in an amount up to 10 wt. %.
18. A refractory brick lining for metallurgical vessels consisting
essentially of a plurality of unburned magnesite-carbon brick, said brick
consisting of the brick of any one of claims 14 to 17.
19. A method of increasing the lining life of metallurgical vessels
comprising forming a lining in said vessels using a plurality of unburned
magnesite-carbon brick consisting essentially of the brick of any one of
claims 14 to 17 and subsequently burning said brick in-situ within the
vessel.
20. The mix of claim 1 wherein said alumina aggregate is tabular alumina
containing about 99% alumina, said carbon containing material is coke,
carbon black, or a mixture thereof in an amount less than 5 wt. %, and
said alloy powder contains at least about 46% B.
21. The mix of claim 20 also containing aluminum, silicon, magnesium, boron
carbide, boron nitride, silicon carbide, or silicon nitride, or
combinations thereof in an amount up to 10 wt. %.
22. The mix of claim 21 wherein said carbonaceous binder is a novolak
resin, a resole resin, tar, pitch, or mixtures thereof.
23. An unburned alumina aggregate-carbon refractory shape formed by shaping
and baking the mix of any one of claims 20 to 22.
24. The refractory shape of claim 23 in the form of a slide gate.
25. The refractory shape of claim 23 in the form of a shroud tube.
Description
BACKGROUND OF THE INVENTION
The present invention relates to carbon-containing refractories and, in
particular, magnesite-carbon refractory brick suitable for use in metal
processing equipment, especially basic oxygen furnaces (BOF) and other
metallurgical vessels wherein the principal mode of wear of the refractory
brick lining is slag attack and where hot strength and high slag
resistance of refractory linings are required. Furthermore, this invention
is applicable to unburned alumina-carbon refractories such as those used
in slide gates and shroud tubes which control the flow of molten steel in
the continuous casting process in which properties comparable to shapes
containing B.sub.4 C are desired.
There is abundant prior art dealing with the use of metals in
carbon-containing refractories. Essentially, the purpose of these metals
is to act as oxygen "getters" which combine with free oxygen before the
oxygen can consume carbon in the refractory. Another purpose of the
powdered metals is to form, under certain conditions, stable carbide
phases which decrease the permeability of the refractory and increase its
strength. U.S. Pat. No. 4,306,030 discloses the use of aluminum, silicon,
and magnesium metal powders. These metals increase the oxidation
resistance of the refractory and have the effect of lowering the
permeability of the brick which makes the entrance of oxidizing gases into
the refractory more difficult. It is also known that these metals can be
effective if used individually or in combination or as alloys in various
combinations.
Prior art also discloses the use of various carbides and nitrides either
used individually or in combination with the three primary metals,
silicon, aluminum, or magnesium. The purpose of these carbides (such as
B.sub.4 C or SiC) or nitrides (such as BN or Si.sub.3 N.sub.4) is to
increase the hot strength or corrosion resistance. U.S. Pat. No.
4,471,059, for example, teaches the addition of 0.3 to 5% B.sub.4 C to a
carbon-containing refractory which contains metal additions such as Al,
Si, Cr, or Ni. U.S. Pat. No. 4,540,675 teaches the use of 1-10 wt. %
B.sub.4 C as an anti-oxidant. B.sub.4 C is effective because it has a
relatively high affinity for oxygen and oxidizes to an oxide. This oxide
then in turn reacts with magnesia, silica or a silicate to produce a
viscous glass film in the refractory which further decreases the
permeability of the refractory. U.S. Pat. No. 4,605,635 shows the use in
carbon-containing refractories of SiB.sub.6. The boron portion oxidizes to
B.sub.2 O.sub.3, which then reacts with magnesia, the silicon portion
which also oxidizes to a silicate and reacts with magnesium borate to form
a lower melting liquid. While the carbonaceous material is better
protected against oxidation, the presence of the silicate results in low
and undesirable hot strengths due to reaction thereof with lime or calcium
silicate impurities in the refractory resulting in very low melting fluid
lime-magnesia-borosilicates. This low strength causes the refractories to
be prone to accelerated wear.
SUMMARY OF THE INVENTION
It is the object of this invention to provide carbon-containing brick of
improved physical properties compared to prior art and carbon-containing
shapes which do not contain additions of B.sub.4 C, but have comparable
physical properties to those shapes containing B.sub.4 C.
Briefly stated, the present invention comprises a mix for forming a
refractory comprising at least about 70 wt. % of a magnesite or high
alumina aggregate, a carbon, a silica-free elemental boron containing
B-Mg-O alloy powder in an amount up to about 10 wt. %, and for each 100
wt. % thereof, from about 1 to 6 wt. % of a carbonaceous bonding agent,
said magnesite containing at least 95% MgO, said alumina aggregate
containing at least about 47.5% alumina, said carbon containing at least
90% carbon, and said alloy containing at least 95% B+Mg+O.
The present invention also particularly comprises a magnesite-carbon mix
for forming a refractory comprising about 70% to 97% wt. % magnesite,
about 3 to 30 wt. % of a carbon, less than 10 wt. % metallic additive
(such as aluminum powder) and 0.05 to 10 wt. % of a silica-free elemental
boron containing B-Mg-O alloy powder and for each 100 wt. % of said
magnesite, carbon and alloy from about 1 to 5 wt. % of a carbonaceous
bonding agent, said magnesite containing at least about 95% MgO, and said
carbon containing at least 90% carbon, and said alloy containing at least
95% B+Mg+O.
The present invention further comprises an alumina-carbon mix comprising
about 70 wt. % or more high alumina aggregate, less than 10 wt. % of a
carbon, less than 10 wt. % metallic additive (such as aluminum powder) and
0.05 to 10 wt. % of a silica-free elemental boron containing B-Mg-O alloy
powder and for each 100 wt. % of said alumina, carbon, and alloy from
about 1 to 6 wt. % of a carbonaceous bonding agent, said alumina aggregate
containing at least about 47.5% alumina, and said carbon containing at
least 90% carbon, said metallic additive of at least 90% purity, and said
alloy containing at least 95% B+Mg+O.
The invention also comprises the resultant refractory shapes and
particularly brick and liners as well as slide gates and shroud tubes for
metallurgical vessels having an increased life using said shapes as
hereinafter set forth.
BRIEF DESCRIPTION OF THE DRAWING
The single figure of the drawing is a graph showing oxidation resistance of
various mixes.
DETAILED DESCRIPTION
The essential component of the instant invention is the B-Mg-O alloy.
As to the alloy, a variety of types containing elemental boron may be used.
One specific alloy found to be effective consists of about 46% amorphous
boron and the balance magnesium borate. Chemically, this alloy assays
about 52% boron, 21% magnesium, and 27% oxygen. Another alloy consists of
about 10% amorphous elemental boron and 90% magnesium borate which occurs
in the phases (2MgO B.sub.2 O.sub.3) and Mg.sub.3 (BO.sub.3).sub.2. This
assays to about 20.4% boron, 34.36% magnesium, and 45.2% oxygen. The
alloys should preferably contain no less than 95% B to Mg, and O and the
preferred particle size of these alloys is -200 mesh. They are stable in
water which is highly unusual for a material containing magnesium. These
alloys do not contain any silicon or silicates and are free boric acid
(H.sub.3 BO.sub.3) or boron oxide (B.sub.2 O.sub.3) which are known to be
very detrimental to the hot strength of magnesite or MgO-C refractories.
The boron alloy may be crystalline or amorphous and contain more than 5 wt.
% boron, preferably more than 10 wt. % boron. Alloys containing more than
75% or 90% boron would be considered cost prohibitive and may have too
great a tendency to oxidize forming an excess of a compound like boron
oxide (B.sub.2 O.sub.3) which in large amounts can be detrimental to the
refractories of the system.
The preferred level of alloy addition to MgO-C refractory brick mixes is
from 0.1 to 1.0 wt. %. At these low levels, improvements in coked
porosity, abrasion resistance after firing to 2000.degree. F. and strength
at 1500.degree. F. are obtained.
As to such MgO-C refractory mixes, they must contain at least 95% MgO,
either deadburned, fused, or a combination thereof, have minimal silica,
lime, and boron oxide impurities and have preferably a CaO/SiO.sub.2
weight ratio above about 2.
As used herein, the term "a carbon" refers to any carbonaceous material
containing at least about 90% carbon. Flake graphite having a carbon
content of at least 90% is preferred or a mixture of such graphite with
carbon black, calcined coke, or other suitable forms of carbon.
Conceivably, flake graphite could be eliminated from the mix and carbon
black, calcined coke, or other suitable forms of carbon could be added as
substitutes.
With respect to the proportion of materials, there should be utilized from
about 8 to 30 wt. % carbon, the bulk of which preferably is in the form of
flake graphite, an optional addition of 0.1 to 8 wt. % metal powder
consisting of aluminum, magnesium, or silicon either used individually or
in combination, a required addition of said boron alloy ranging from 0.05
to 10 wt. %, an optional addition of a carbide such as boron carbide or
silicon carbide or a nitride such as boron nitride or silicon nitride
ranging from 0.1 to 8 wt. % and the balance of the mix a relatively high
purity deadburned magnesite having a magnesia content of at least 95%.
The particle size or the graded size of the deadburned magnesite and the
flake graphite is not critical; it should be that conventionally used in
making this type of brick.
As to the aluminum, magnesium, and silicon powders or alloy combinations
thereof the particle size is not critical and, again, it can be of a
graded size conventionally used in making metal-containing brick. It is
critical not to permit the metal amounts to get too high in order to avoid
the possibility of fluxing action that may be caused by oxidized aluminum
and increased porosity that can be caused by volatilized magnesium.
As to the optional carbides and nitrides they may be of any size,
preferably -65 mesh, that are conventionally used in refractory brick.
Also included in the mix must be a carbonaceous bonding agent that yields
high levels of carbon during pyrolysis, i.e., over 35 wt. % carbon.
Examples are any novolak or resol resin, tar, pitch or mixtures thereof.
At the temperatures at which these brick are used, these materials are
decomposed and the resulting carbon char acts to bind the brick. The
amounts of binder are not critical, but it is desired to avoid high binder
levels in order to prevent cracking of the shape and to maintain adequate
handling strength at the press. Ordinarily, about 1.5 to 6 wt. %,
preferably 2.5 to 4 wt. %, of such bonding agent is added for each 100% by
weight of the mix.
The method of forming the brick is not critical in that the components
noted above can simply be admixed, pressed into shape using typical
brick-making presses, and then baked at about 250.degree.-550.degree. F.
to form unburned brick which are then used to form linings for
metallurgical vessels. Optionally, the brick may be tar impregnated. In
use, the brick are exposed to high temperatures under reducing conditions
which forms carbon bonded brick of improved physical properties.
The brick of the present invention are particularly suitable as linings for
basic oxygen furnaces.
The brick of the present invention are made to the size and shape required
to form the entire lining or a portion of the lining of any shape
metallurgical vessel. The linings are formed in the conventional manner by
using brick, ramming mix, vibration cast mixes, or castables which contain
this special boron alloy.
As to the high alumina aggregate, it is necessary that it contain at least
47.5% alumina and comprise at least 70 wt. % of the mix. The aggregate may
be calcined or fused. The preferred aggregate is tabular alumina which
typically contains about 99% alumina. The size of the high alumina
aggregate is not critical but should be of a graded size typically used in
brick making.
The preferred carbon for use with the high alumina aggregate is in the form
of -150 mesh coke or carbon black in amounts less than 5 wt. %, preferably
less than 4 wt. %.
The preferred metallic addition for the high alumina aggregate mix is
aluminum, sized -28 mesh, in amounts less than 10 wt. %, preferably less
than 5 wt. % of the mix.
As to the boron alloy used with the high alumina aggregate mix, both types
which were previously described may be employed in amounts previously
stated. However, to maximize hot strength at 1500.degree. F. use of the
higher boron alloy (B=46%) is preferred. The mix may contain an optional
carbide or nitride, preferably -65 mesh, and in amounts less than 10 wt.
%, that are conventionally used in refractory brick. This mix also
contains a carbonaceous bonding agent as was previously described.
The mixes are formed into shapes such as slide gates or shroud tubes by
adding the admixed components to the desired molds and pressing the
shapes. After removal from the mold the shapes are cured and may be
optionally tar impregnated and then baked under reducing conditions to
remove the bulk of the volatiles from the tar.
The invention will be further described in connection with the following
examples which are set forth for purposes of illustration only.
EXAMPLES 1 TO 7
A series of seven MgO-C compositions were made using the components and
proportions as set forth in Table I below. The brick were made by pressing
at about 18,000 psi and then cured using a curing schedule of 100.degree.
F./hr. to 350.degree. F. with a three hour hold, and then tested for the
usual physical properties as set forth in Table I.
TABLE I
__________________________________________________________________________
Effect of Special Boron Alloy Compared to B.sub.4 C
Example 1 2 3 4 5 6 7
__________________________________________________________________________
Mix:
Deadburned Magnesite
81.0%
80.9%
80.75%
80.5%
80.9%
80.75%
80.5%
Flake Graphite 17.0 17.0 17.0 17.0 17.0 17.0 17.0
Aluminum Powder 2.0 2.0 2.0 2.0 2.0 2.0 2.0
Boron Carbide Powder
-- 0.1 0.25 0.5 -- -- --
Special Boron Alloy Powder
-- -- -- -- 0.1 0.25 0.5
(46% B)
Phenolic Resin 3.7
Bulk Density at Press, pcf
183 183 183 183 183 182 182
Bulk Density After Baking, pcf
181 180 180 179 180 180 180
Data From Porosity (After Coking)
Bulk Density, pcf 173 173 173 172 173 174 174
Apparent Porosity, %
9.4 9.4 8.7 8.8 8.9 8.2 8.0
Apparent Specific Gravity
3.06 3.06 3.04 3.03 3.05 3.03 3.02
Modulus of Rupture, psi
At 1500.degree. F..sup.1
20 20 110 150 60 260 330
At 2000.degree. F..sup.2
2250 2340 2380 2740 2540 2860 2610
Crushing Strength at 280.degree. F..sup.2
4270+
5030+
4830+
4100+
5700+
4450+
4560+
Number of Samples that Broke in Test
3 2 0 0 3 0 1
Modified ASTM C-704 Abrasion Test
68 60 54 48 50 47 40
After 2000.degree. F. Reheat.sup.1,3
Volume Eroded, cc:
__________________________________________________________________________
.sup.1 Oxidizing Atmosphere
.sup.2 Reducing Atmosphere
.sup.3 500 grams of SiC were used
+Indicates a strength that is greater than what is shown
A comparison of mixes 1 to 4 indicate that additions of 0.1 to 0.5 wt. %
fine boron carbide to an aluminum-containing magnesite brick of the 20%
carbon class, as taught by prior art, resulted in slightly progressive
decreases in apparent porosity after coking, slight increases in strength
at 1500.degree. F., and a noticeable improvement in resistance to crushing
at 2800.degree. F. which is reflected in fewer samples breaking in the
crushing test as the amount of B.sub.4 C increases. This series also
showed a modest improvement in abrasion resistance after being heated to
2000.degree. F.
A comparison of mix 1 with mixes 5, 6, and 7, which define our invention,
shows the effect of adding 0.1 to 0.5 wt. % boron alloy powder. This
addition has a more dramatic effect than boron carbide on decreasing
apparent porosity. As little as 0.5 wt. % boron alloy decreases apparent
porosity 1.4% which is considered significant. In addition, this additive
clearly produces better strength at 1500.degree. F. under oxidizing
conditions than what is produced by an equivalent amount of boron carbide.
This suggests that a pressed shape containing this boron alloy may have
better oxidation resistance than a mix containing B.sub.4 C as more of the
bond is retained after this test. As little as 0.25% of boron alloy
appears to produce higher strength at 2000.degree. F. as does 0.25 or even
0.5 wt. % boron carbide. This special alloy, like B.sub.4 C, also produces
the desirable tendency of increased strength at 2800.degree. F. as
reflected by a decrease in the number of test samples which broke during
the crushing test. More significantly, increasing amount of the special
boron alloy clearly increased the abrasion resistance of the shapes after
heating to 2000.degree. F. This too may reflect an increase in oxidation
resistance for pressed shapes containing the boron alloy.
EXAMPLES 8 TO 10
An additional test was conducted to contrast the difference between mixes
containing boron carbide and mixes that contain the boron alloy. To
accomplish this 5/8" diameter, 2" long samples of cured brick made of the
mixes of Examples 1, 3, and 6, respectively, shown in Table I were exposed
to 1.5% oxygen in argon in a furnace which was heated at 500.degree.
F./hr. to 2000.degree. F. with a hold time of 4 hrs. As carbon burned, all
forms of carbon and oxygen were converted to carbon dioxide by passing the
gases over cupric oxide (CuO) and detecting the amount of carbon dioxide
formed by using an infra-red CO.sub.2 analyzer. FIG. 1 shows that the mix
with the boron alloy tended to produce the least loss of carbon especially
between the third and fourth hour of combustion. However, at the end of
the test (Table II) the sample with the boron alloy imparted essentially
the same oxidation resistance as the mix containing boron carbide. These
results stand in contrast to the 1500.degree. F. MOR test and the abrasion
test which indicated a possible improvement in oxidation resistance.
TABLE II
______________________________________
Weight Changes During Oxidation Test
Example 8 9 10
______________________________________
Initial Weight (g)
27.5887 27.7673 28.1019
Final Weight (g)
25.4926 25.7417 26.0710
Weight Loss (g)
2.0961 2.0256 2.0309
Weight Loss (%)
7.6 7.3 7.2
______________________________________
It is not clearly understood why this boron alloy provides improved
intermediate strength and lower porosity compared to similar mixes
containing boron carbide. It is speculated that at these intermediate
temperatures a viscous boron-magnesium-oxide glass forms which lowers the
apparent porosity and produces a secondary bond which imparts into the
shape higher strength. Apparently, the high temperature properties of this
glassy phase is quite exceptional as evidenced by the high strength values
at 2800.degree. F.
EXAMPLES 11 AND 12
High alumina mixes were made, one containing the boron alloy and another
containing boron carbide. The mixes were made in the conventional manner
used to make slide gates. The batches were mixed with resin and then
pressed. The slide gates were cured to harden the resin binder and then
the plates were tar impregnated followed by baking at 1000.degree. F. The
mix formulations, processing conditions, and test results are set forth in
Table III below.
As shown by the data the addition of 1% boron alloy for 1% boron carbide
resulted in essentially equivalent physical properties.
TABLE III
______________________________________
Resin Bonded Alumina-Carbon Mixes
Example 11 12
______________________________________
Mix:
Sintered Alumina, 6/10 mesh
10% 10%
Sintered Alumina, 10/24
36 36
Sintered Alumina, 24/48
10 10
Sintered Alumina, -48
15 15
Sintered Alumina, -325
12 12
Reactive Alumina, -325
10 10
Aluminum Powder 3 3
Fine Coke, 65/375 2 2
Carbon Black, -325 1 1
Boron Carbide 1 --
Boron Alloy (B = 46%)
-- 1
Plus Addition 3.7 3.7
Resin
Forming Pressure, psi
15,000
Bulk Density at Press, pcf
197 196
Cured at 350.degree. F., 4 hrs.
Tar Impregnated, Baked
at 1000.degree. F., 4 hrs.
Bulk Density, pcf 195 195
Apparent Porosity, % 7.8 8.5
Apparent Specific Gravity
3.39 3.41
Modulus of Rupture, psi
At Room Temperature, (Av. 3)
2990 2540
At 1500.degree. F. (oxidizing) (Av. 2)
1910 1510
At 2000.degree. F. (reducing) (Av. 3)
4600 5130
Modulus of Elasticity, .times.10.sup.6 psi
10.9 10.3
______________________________________
As shown by the data the addition of 1% boron alloy for 1% boron carbide
resulted in essentially equivalent physical properties.
All the mesh sizes set forth herein are Tyler mesh sizes.
While the invention has been described in connection with a preferred
embodiment, it is not intended to limit the scope of the invention to the
particular form set forth, but, on the contrary, it is intended to cover
such alternatives, modifications, and equivalents as may be included
within the scope of the invention as defined by the appended claims.
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